Ultrasound technology

How Stimshop ultrasound works

  • Ultrasonic communication is a complementary technology for indoor telecommunications at close and medium range.
  • Acoustic waves are elastic waves that spread into a physical environment (air, water, steel, etc.). Passing from an environment to another only allows an infinitesimal part of the wave to go through. They are perfectly suited to perform localized and secured communications
  • Near-ultrasounds are located in the approximated area between the audible spectrum and the ultrasounds (~16−30 kHz).  Therefore, smartphones can be used as transcievers, without any hardware modification, to receive and send airborn signals

fig 1: Acoustic Propagation and reflections in a Room


fig 2: Near-Ultrasounds Spectrum

Technological issues

Sending data, of any length, via sound is a true challenge, especially in comparaison of radio-frequency communication (RF). There are the five main issues encountered

  1. The ambient noise level is often closer or greater than your signal (low SNR : Signal to Noise Ratio), hence jamming and disrupting the sent data.
  2. The attenuation of airborn acoustic waves is proportional to the distance between the transmitter (Tx) and the receiver (Rx) : distance increases the SNR.
  3. Doppler Effect is significant and can change the frequency of the signal, proportionally to the moving speed of Tx or Rx.
  4. The frequency interval available is rather thin compared to RF : only a few kHz.
  5. The bandwidth or bit-rate is very low and does not permit any high-speed data transmission.
STIMSHOP unique solution

To go over those issues, Stimshop has developed a unique and patented solution to provide a reliable near-ultrasonic airborn communication, by using chirps and FHSS.

With a specific modulation, that has proven itself in applications like RADAR or under-water communications, paired with a custom encryption, we can provide robust communications

The robustness of our signals counters Doppler Effect, allows perfect decryption in noisy environments and transmits over a distance of approximately 80 meters (with a 2x7 Watts transmitter) a mean of 100 bits/second.

Our unique communication system allows also a single transmitter to communicate with multiple receivers (SIMO communication) without any interference. This is made possible by frequency multiplexing.

Fig 3: SIMO Communication System

With a PhD student in its rank and tight relations with academics and researchers, STIMSHOP is continuously working for improving  near-ultrasonic airborn communication. 


STIMSHOP solution’s advantages

This unique solution, that we master end-to-end, allows us to offer two types of products, fully customizable


Based on CSS (_Chirp Spread Spectrum_ or chirps), on 5 channels, it is mainly made for smartphone communications and identification.

Typical signal:


Based on FHSS (Frequency-Hopping Spread Spectrum), half-duplex on 2 channels, it is mainly made for data transfer and industrial uses.

Typical signal:

Protocols comparison

Many digital modulations exist to encode data into a signal. We chose our modulations in the Spread Spectrum categorie to ensure their robustness. We compare them with some well known modulation : Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK) – specifically Dual-Tone Multi-Frequency (DTMF) – and Phase Shift Keying (PSK).


A few other companies also provide ultrasonic communications, but none as robust as STIMSHOP’s. We give an overview of our solution in comparison to some well known RF protocols.  

Fig 4: Ultrasonic communication systems comparison in range capacitiy. Fig 5: STIMSHOP and RF communication systems comparison in bit-rate, range and cost.